Development of natural habit of large free-nucleated AlN single crystals

Well‐shaped freestanding crystals of aluminum nitride up to 25 mm in length have been grown in tungsten crucibles using physical vapor transport (PVT) method. The platelet crystals exhibit characteristic asymmetric habit with largest flat being a pseudo‐facet build by alternating (10$ \bar 1 $0) facets. Pronounced true facets are Al‐terminated (0001) and adjacent {10$ \bar 1 $2} facets, with one of them growing much larger than others. The analysis of formation history of freestanding AlN crystals made it possible to explain their habit, very unusual for wurtzite‐type structure. Growth of freestanding AlN starts from a long needle formed along the [11$ \bar 2 $0] direction at lower temperature of 1900–2000 °C and continues by needle expansion and thickening along mainly [0001] direction, leading to asymmetric platelet. In such geometry only one extended (10$ \bar 1 $2) facet can be developed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)